1. Field of the Invention
This invention relates to sheet roofing systems.
2. Description of Prior Art
Traditionally many roofs, especially roofs of large buildings such as arenas, barns, industrial warehouses and the like, have been made from sheet metal material. Sheet metals tend to be expensive and are difficult to handle especially in high winds. Joins between the sheets have needed special waterproofing techniques. When the metal sheets are intended to be especially decorative rather than merely utilitarian, the expense is even greater. Frequently such decorative metal sheets may be formed of copper.
While metal roofing systems have not been superseded it has become relatively common to use, in their place, roofing systems in which the covering material is a flexible plastics material. Frequently the plastics material is ethylene propylene diene monomer (EPDM) rubber. Alternatively it maybe polyvinyl chloride (PVC). Either of these materials may be coloured either to mimic the colourings of natural metal roofing systems or in other colours that can only be achieved on metal by means of paint.
In one respect, metal sheeting may have some small advantage over the conventional use of plastic sheet in that metal sheeting may be provided with molded decorative ribs and grooves or other decorations. This type of decoration cannot conveniently be molded into flexible plastic sheeting in the same way as is possible for semi-rigid or rigid metal sheet. It is necessary to superimpose simulated decoration on roofs clad with plastic sheet.
The sheet may be applied to a roof subsurface, for example plywood, chipboard or other flat surface, by one of two conventional processes. The first of these is the mechanical fixing system in which the plastic sheet is laid over the subsurface and fixed around its edges by means of nails, screws, etc. The adjacent sheet overlaps the first sheet slightly and is similarly fixed around its edge or it may be welded or adhered to the edge of the first sheet. The second system is the fully adhered system in which the plastic sheet is adhered to the subsurface over its whole surface and is welded to the adjoining sheet at its edge to form a single integral sheet over the whole roof. While the mechanical fixing system and the fully adhered system may be regarded as equivalent, the fully adhered system may be preferable in that the resultant roof covering is totally waterproof and closely adhered to the subsurface so that there is no possibility of fluttering, or other movement of the sheet in high winds. This system, however, is not always possible, for example when using EPDM or other sheets which do not weld to one another and, therefore, various proposals have been made for waterproofing the joints between plastic sheets. These proposals generally are applicable to EPDM since there is little difficulty in welding PVC to form integral wholly waterproof sheets. Nevertheless, there is no reason why a mechanical fixing system may not be used with PVC if it is so desired.
Exemplary of a mechanical fixing system at the edge of sheets which is intended to provide both mechanical fixing and waterproofing and, possibly, some decorative ridging, is the system described and claimed in U.S. Pat. No. 5,168,684 issued Dec. 8, 1982 to Bruhm. The system described apparently includes longitudinal battens locating the respective edges of plastic sheets and disks holding the battens and sheet edges in place by means of fixing screws which pass right through the subsurface into a roof truss. Similarly U.S. Pat. No. 5,161,342 issued Nov. 10, 1992 to Hasan et al discloses simple battens and screws providing a mechanical fixing system for a plastic sheet. U.S. Pat. No. 4,833,853 discloses yet another mechanical fixing system in which an elongated mounting bracket through which a fixing screw extends, provides a grip for a cover member. The mounting bracket is of complex form and the edges of overlapping sheets are drawn up to cover the head of the screw. U.S. Pat. No. 4,389,826 issued Jun. 28, 1983 to Kelly shows another patent system for mechanical fixing of a flexible roofing sheet.
Exemplary of patents concerning semi-rigid or rigid roofing sheets are U.S. Pat. No. 4,366,465 issued Jan. 4, 1983 to Simpson and U.S. Pat. No. 4,269,012 issued May 26, 1981 Mattingly et al.
The present inventor has addressed the problem of providing a decorative finish strip for a flexible sheet roofing system irrespective of whether the roofing system is installed by the mechanical fixing method or by the fully adhered system. The present inventor has also addressed the problem of providing simplicity of installation with a minimum number of parts; the provision of a base strip which may be used for mounting a variety of different finish strips; and the need to keep the installation inexpensive by minimizing labour costs and part costs.
The mechanically fixed system requires a fastening bar or disc around the perimeter in the sheet or at any change in elevation or around protrusions. One of its main advantages is that it may be done at any time of year and is not dependent on the temperature at which the adhesive may be laid. The fully adhered system, on the other hand, can conform to any configuration but may be dependent upon temperature which influences the drying time of the adhesive.